A turbofan gas turbine engine used for powering an aircraft in flight typically includes a fan assembly having a plurality of circumferentially spaced apart fan blades each having a dovetail disposed in a complementary, axially extending dovetail groove in the perimeter of a rotor disk. The dovetail grooves are defined by dovetail posts and are complementary in configuration with the blade dovetails for radially retaining the blades to the rotor disk. The blades are also axially retained in the rotor disk by conventional forward and aft blade retainers which prevent axial movement of the blades in the upstream and downstream directions.
The normal axial loads carried to the rotor disk by the blade dovetails are relatively small. These loads include primarily the aerodynamic thrust loads developed by the fan blades, and vibratory loads thereof. However, the engine is also subject to ingestion of relatively large birds, or a blade-out occurrence wherein one of the fan blades is severed from the rotor disk, which generates relatively large axial forces upon impact with adjacent blades. The large bird or severed blade is accelerated in the downstream direction by impact with the adjacent blades which imposes a relatively large force in the axial upstream direction.
Accordingly, the forward blade retainer is conventionally designed for accommodating the relatively large axial forces associated with a large bird or blade-out impact which necessarily requires a large forward blade retainer as well as correspondingly sized dovetail posts for reacting the large axial force within suitable stress limits. In turn, this results in an undesirable increase in weight of the fan assembly.